Mass spectormeter



June 10, 1958 J. G. sKlNNER MASS sPEcTRoMETER 2 sheds-sheet 1 Filed NOV.lO, 1955 INVENTOR.

J. G. SKINNER HU@ f (fw/a/ ATTORNEYS United States Patent MASSSPECTROMETER John G. Skinner, Corvallis, Greg., assigner to PhillipsPetroleum Company, a corporation of Delaware l Application November 10,1955, Serial No. 546,221

' 8 Claims. (Cl. Z50-41.9)

This invention relates to sample inlet and evacuation systems for massspectrometers. In another aspect it relates to electrode mounting meansfor vacuum tubes.

In recent years mass` spectrometers have been developed from highlyspecialized academic research instruments for measuring the relativeabundance of isotopes into analytical tools of eXtreme sensitivity andaccuracy. At the present time, applications are being found for the useofimass spectrometers in process monitoring and control. Massspectrometry comprises, in general, ionizing a sample of material underinvestigation and separating theresulting' ions accordingr to theirmasses to determine the relative abundance of ions of selected masses.The material to be analyzed usually is provided as a gas which isbombarded by a stream of electrons to produce thedesired ions. Althoughboth positive and negative ions may be formed by such electricalbombardment, most mass spectrometers make use of only the positiveions.` These positive ions are accelerated out of the region of theelectron beam by means of negative potentials. Suchrz'potentials impartequal kinetic energies to ions having like charges such that ions ofdifferent` masses have 'different velocities after passing throughl theelectrica'llieldl and, consequently, have different momenta.

An important feature of the present inventionresides in :Q1-#combinationsample inlet and evacuation system for a mass spectrometer whichminimizes thenumlaerof` glassto-met'al seals in the tube. This isimportant to reduce leak' possibilities. The vacuum pump inlet is`connected by a metal tube to the glass spectrometer tube. sample inletconduit lextends into the tube -through the evacuation outlet'. Anotherfeature of thisA invention resides 'inV an electrode mounting structurewhich eliminate's microphonics. The collector plate is secured'l to ashield plate so` as to engage a plurality of spring biased spacer balls.This provides a flexible assembly which can accommodate temperaturefluctuations.

Accordingly, it is an object of thisrinven'tion to provide an improvedsample inlet and evacuation system for a mass spectrometer. 4 y

A further object is to lprovide improved electrode mounting meansfor usein vacuum tubes.

Other objects, advantages'and features 'of this inven- V tion shouldbecome apparent from the following detailed description taken inconjunctionrwith Vthe accompanying drawing in which:

Figure l is a 'schematic representation-of a mass spectrometerincorporating features of this invention;

Figure 2 is a detailedview of the collector plate mounting assembly; and

Figure 3 is a detailed view of the sample inlet and tube evacuatingsystem.

Referring now to the Vdrawing in detail and to Figure linvparticul'ar,there is shown a mass spectrometer tube comprising a gas impermeableenvelope, the interior of which is maintained at a reduced pressure by avacuum pump, not shown, which communicates with the interior The 'ice

of tube 10 through a'conduit 11. A sample of gas to be analyzedA isdirected into tube 10 through a conduit 12. An electron emittingfilament 13 is disposed inr one end of tube 10 and an ion vcollectorplate 14 is disposed in the secondend of the tube. The end terminals offilament i3 are connected to the respective end terminals of thesecondary winding 15 of a transformer 16. The'end terminals of theprimary winding 17 of transformer 16 are connected to an alternatingcurrent source 13. The center tap of the secondary Winding 15 oftransformer i6 is connected to a negative potential terminal 19.

The gas sample supplied through conduit 12 diffuses into an ionizationchamber 22 in tube 10 which is defined by a pair of spaced gridsfZS and24 that are maintained at ground potential. Electrons emitted fromfilament 13 are accelerated into chamber 22 by the potential. differencebetween filament i3 and grids 23 and 24, A grid 26 is-positionedbetweenfilament 13 and grid 23. Grid 26 is connected to the output of anemission regulator circuit 27, while can be of the type disclosed in thecopendingapplication of `M. C. Burk, Serial No. 412,790, filed February26, 1954, now U .S. Patent No. 2,792,500. The input of emissionregulatorV 27 is connected to the center tap of transformer Winding '15.This emission regulator is provided for the purpose of applying apotential to grid26-of magnitude such as to maintain a constant flow ofelectrons into ionization chamber 22 irrespective of minor fluctuationsin the electron emission from filament 13. In thismanner the rate atwhich gas molecules are ionized in chamber 22 byA electron bombardmentis afunction of only the gas pressure in the chamber.

Y'A first collimating electrode 28' is positioned on the second side ofionization chamber 22 and is connected to the contact'or of apotentiometerZil. One end terminal of potentiometer 2t) is connected toaA negative potential terminal 2l, the second end terminal ofpotentiometer 2li being" grounded. A secondcollimating electrode 23" isspaced from electrode 28. Electrode 28 is connected to the'conta'ctor ofa'potentiometer 2li. The end' terminals of potentiometer 2li areconnected to terminal' 21 and ground, respectively.

The positive ions produced in ionization chamber 22` are accelerated bythe negative potentials'applied to electrodes 28and` 28 so as to travelthrough the'tube toward collector plate 14. A first set of three equallyspaced grids 35, 36 and 37 is positioned in tube l@ between grid 28 andcollector plate i4; a second set of equally Vspaced gridsy 38, 39 and4l? is positioned in spaced` relation with the first set of grids; athird set of equally spaced grids 42, 43 and 44 is positioned in spacedrelation with the secondset of grids; a fourth set of equallyspacedgrids 4S, 46 and-47 is positioned in spaced'rela` tion with thethird set of grids; and a fifth set of equally spaced grids49, Sil and5l is positioned in .spaced relation with the fourth setV of, grids.Gridy 35" is connected tothe contacter of a potentiometer 29. One endterminal of potentiometer 29 is connected to a negative potentialterminal 3o, the second end terminal of potentiometer 29 being connectedto ground. The contactor of potentiometer 29 can bey adjusted to applyselected. negative accelerating potentials to grid 3S. Grids 36, 39, 43,46 and 50 are connected to one another and to the output terminal of anelectronic switch 55. The input terminal of switch 5S is connected toone output terminal of ay radio frequencyoscillator S6. 'Switch 55 iscontrolled by the output of a square wave generator 57, which in turn isenergized by the output of an audio oscillator 5S. Switch 55 is thusturned on and off at the frequency of oscillator Sato apply the outputVof` oscillator 56 to grids 36, V39,. 43, 46 andvSti. Grid35 is connectedto one output terminal of a step back detector 61, which in turn isconnected to an output terminal of oscillator 56. The second outputterminal of detector 61 is connected to grid 51. Grids 35 and 51 areconnected to one another by a voltage dividing network 63 whichcomprises five resistors 64, 65, 66, 67 and 68 that are connected inseries relation. Grids 37 and 38 are connected to one another and to thejunction between resistors 64 and 65; grids 40 and 42 are connected toone another and to the junction between resistors 65 and 66; grids 44and 45 are connected to one another and to the junction betweenresistors 66 and 67; and grids 47 and 49 are connected to one anotherand to the junction between resistors 67 and 68.

A plurality of closely spaced stopping grids 70 is positioned betweengrid 51 and collector plate 14. Grids 70 are connected to one anotherand to the output of a stopping detector 71, which in turn is connectedto an output of oscillator 56. A plurality of suppressor grids 72 ispositioned between grids 79 and collector plate 14. Grids 72 areconnected to a negative potential terminal 73 to suppress secondaryelectrons which may result from ions impinging upon metal parts of thetube. A grounded shield 75 is positioned adjacent collector plat 14.

Collector plate 14 is connected to one inputV terminal of an amplifier76 which is tuned to pass signals of the same frequency as the frequencyof oscillator 58. The second input terminal of amplifier 76 is connectedto ground. The output terminals of amplifier 76 are connected to firstinput terminals of a phase detector 77. The second input terminals ofphase detector 77 are connected to output terminals of oscillator 58.The output terminals of phase detector 77 are connected to a suitableindicating means such as a recorder 78.

The circuits illustrated schematically in Figure 1 are described indetail in the copending application'of M. C. Burk and F. W. Karasek,Serial No. 480,698, filed January 10, 1955, now U. S. Patent No.2,761,974. i

Details of the collector plate assembly are illustrated in Figure 2.Plate 14 is attached by a hub 110 and a screw 111 to a support rod 112.Screen plate 75 has an elongated tube 113 integral therewith which fitson a tube 114 that is sealed to spectrometer tube end 104 at its outerend. Rod 112 is sealed in tube 114 by a plug 115. Plate 75 has aplurality of openings 117 therein. An annular spring 118 is weldedtoplate 75 so as to extend through openings 117. The portions ofspring'118 which extend through the openings in plate 75 form seats toreceive insulating balls 120. Balls 120 engage plate 14. Tubes 113 and114 are held together by a clamp 121. 'In constructing the massspectrometer tube, tube 114 is sealed into glass member 104. Rod 112 issealed in plug 115. Tubes 113 and 114 are then pushed together so thatpate 14 engages balls 120 and are secured in place by clamp 121.' It hasbeen found that this particular structure is durable and eliminatesmcrophonics. Glass end 104 is sealed to the remainder of the tube afterthe grid structure is inserted.

The sample inlet tube evacuation system is illustrated in Figure 2. Ametal sleeve 125 is sealed to a glass nipple 126 of tube 10. There areonly two glass-tometal seals in the system. This minimizes the danger ofleaks. A third seal is required if the filament is removable, asillustrated. A rst flange 127 is welded to sleeve 125. A second fiange128 is welded to an outlet pipe 11 which communicates with a vacuumpump, not shown. An annular plate 130 is positioned between anges 127and 128 and is secured in place by a plurality of bolts 131. Gaskets 132and 133 are employed to make a tight seal. Gas sample inlet tube 12 iswelded to and extends through plate 130. The inner end of tube 12extends into yspectrometer tube 10. The gas to be analyzed diffuses fromtube 12 into the ionization chamber.

"From the foregoing description of a preferred embodiment of thisinvention, it should be apparent that there is provided a massspectrometer tube having several improvements. The gas sample isintroduced and the tube is evacuated through a single opening. Thisreduces the danger of leaks developing. The collector plate ispositioned by a novel mounting structure which remains firm despitetemperature changes in the tube and which eliminates microphonics.

While the invention has been described in conjunction with a presentpreferred embodiment, it should be evident that it is not limitedthereto.

What is claimed is:

l. A mass spectrometer comprising a glass envelope having an openingtherein, a first metal tube sealed to said envelope to communicate withsaid opening, a first flange on the end of said first tube remote fromsaid envelope, a second tube having a flange at one end thereof, thesecond end of said second tube Vbeing adapted to be connected to avacuum pump, a plate having an opening therein, means to seal said platebetween said anges, a third tube extending from a region exterior ofsaid envelope through said plate and said first tube to the interior ofsaid envelope, said second tube being sealed in said plate and beingadapted to introduce a sample of gas to be analyzed into said envelope,means toV ionize the gas sample, a collector plate in said envelope, andmeans to direct ions of predetermined mass to said collector plate.

2. A charged particle collector assembly comprising a support platehaving a plurality of openings therein, a spring attached to said plateand extending through said openings, an ion collector plate, a spacerpositioned adjacent each of said openings in engagement with saidspring, and means securing said collector plate to said support plate sothat said collector plate engages said spacers against the force of saidspring.

3. Apparatus to introduce a gas sample into and to evacuate a massspectrometer tube comprising conduit means sealed to the spectrometertube to communicate at one end with the interior thereof, the second endof said conduit means being adapted to be connected to a vacuum pump,and a tube to supply a gas sample extending from a region exterior ofsaid spectrometer tube to the interior thereof through at least aportion of said conduit means.

4. A charged particle collector assembly comprising a first tube, a rodextending through said first tube, sealing means mounting said rod insaid first tube in spaced relationship therewith, a collector plateattached to one end of saidv rod, a second tube enclosing at least aportion of said first tube, a second plate secured to the end of Vsaidsecond tube adjacent said collector plate, said second plate having aplurality of openings therein, a spring attached to said second plateand extending through said openings toward said collector plate, aspacer positioned adjacent each of said openings in engagement with saidspring, and means to secure said second tube to said first tube so thatsaid collector plate engages said spacers against the force of saidspring.

5. The combination in accordance with claim 4 wherein each of saidspacers comprises a sphere of insulating material.

6.V A mass spectrometer comprising a gas impermeable envelope defining aspectrometer tube, conduit means sealed to the spectrometer tube tocommunicate at one end with the interior thereofthe second end of saidconduit means being adapted'to be connected to a vacuum pump, a tube tosupply a gas sample extending from a region exterior of saidspectrometer tube to the interior thereof through at least a portion ofsaid conduit means, means to ionize molecules of gas supplied to saidspectrometer tube, a support plate in said spectrometer tube, having aplurality of openings therein,

' a spring attached to said plate and extending through said openings,an ion collector plate, a spacer positioned adjacent each of saidopenings in engagement with said spring, means securing said collectorplate to said support plate so that said collecter plate engages saidspacers against the force of said spring means to direct ions ofpredetermined mass to said collector plate, and means to measure ionsimpinging upon said collector plate.

7. A mass spectrometer comprising a glass envelope having an openingtherein, a first metal tube sealed to said envelope to communicate withsaid opening, means to attach ,a vacuum pump to said iirst tube, asecond tube extending through at least a portion of said rst tube intosaid envelope through said opening to introduce a sample of gas to beanalyzed, means to ionize molecules of gas supplied to said spectrometertube, a support plate in said spectrometer tube having a plurality ofopenings therein, a spring attached to said plate and extending throughsaid openings, an ion collector plate, a spacer positioned adjacent eachof said openings in engagement with said spring, means securing saidcollector plate to said support plate so that said collector plateengages said spacers against the force of said spring, means to directions of predetermined mass to said co1- lector plate, and means tomeasure ions impinging upon said collector plate.

8. A mass spectrometer comprising a glass envelope having an openingtherein, a rst metal tube sealed to said envelope to communicate withsaid opening, a rst flange on the end of said iirst tube remote fromsaid envelope, a second tube having a second flange at one end thereof,the second end of said second tube being 30 2,768,301

6 adapted to be connected to a vacuum pump, a plate having an openingtherein, means to seal said plate between said flanges, a third tubeextending from a region exterior of said envelope through said plate andsaid rst tube to the interior of said envelope, said second tube beingsealed in said plate and being adapted to introducea sample of gas to beanalyzed into said envelope, a third tube secured to said envelope andextending into said envelope, a rod extending through said third tube,sealing means mounting said rod in said third -tube in spacedrelationship therewith, a collector plate attached to the inner end ofsaid rod, a fourth tube enclosing at least a portion of said third tube,a second plate secured to the end of said fourth tube adjacent saidcollector plate, said second plate having a plurality of openingstherein, a spring attached to said second plate and extending throughsaid openingstoward said collector plate, a spacer positioned adjacenteach of said openings in engagement with said spring, means to securesaid fourth tube to said third tube so that said collector plate engagessaid spacers against the force of References Cited in the tile of thispatent UNITED STATES PATENTS Bennett Oct. 28, 1956

